WASHINGTON — Fewer than two-thirds of the former soldiers being reactivated for duty in Iraq and elsewhere have reported on time, prompting the Army to threaten some with punishment for desertion.

The former soldiers, part of what is known as the Individual Ready Reserve (IRR), are being recalled to fill shortages in skills needed for the conflicts in Iraq and Afghanistan.

Of the 1,662 ready reservists ordered to report to Fort Jackson, S.C., by Sept. 22, only 1,038 had done so, the Army said Monday. About 500 of those who failed to report have requested exemptions on health or personal grounds.

"The numbers did not look good," said Lt. Col. Burton Masters, a spokesman for the Army's Human Resources Command. "We are tightening the system, reaching the people and bringing them in."

Masters said most of the requests for exemptions are likely to be denied: "To get an exemption, it has to be a very compelling case, such as a severe medical condition."

The figures are the first on the IRR call-up. They reflect the challenges the Pentagon faces in trying to find enough troops for ongoing operations and show resistance among some servicemembers who returned to civilian life.

The ready reserve is an infrequently used pool of former soldiers who can be called to duty in a national emergency or war. On June 29, the Army announced it would call 5,674 members of its IRR back to active duty this year and next.

Several of those who received recall notices have already been declared AWOL (absent without official leave) and technically are considered deserters. "We are not in a rush to put someone in the AWOL category," Masters said. "We contact them and convince them it is in their best interests to show up. If you are a deserter, it can affect you the rest of your life."

Fourteen people were listed as AWOL last week; six subsequently told the Army they would report. Punishment for being AWOL is up to the unit commander and can include prison time and dishonorable discharge, said Col. Joseph Curtin, an Army spokesman.

With a force that generals say is stretched thin, the Army is considering $1,000-a-month bonuses to ex-soldiers who volunteer to return for overseas duty.

Ready reservists are soldiers who were honorably discharged after finishing their active-duty tours, usually four to six years, but remain part of the IRR for the rest of their original eight-year commitment. The IRR call-up is the first major one in 13 years, since 20,277 troops were ordered back for the Persian Gulf War.